This disclosure relates to a vaporized fuel processing apparatus having a stepping motor type closing valve for opening and closing a path connecting a fuel tank with a canister.
Japanese Laid-Open Patent Publication No. 2001-214817 discloses a conventional vaporized fuel processing apparatus having a path connecting a fuel tank with the internal combustion engine and configured to supply vaporized fuel from the fuel tank into the internal combustion engine. When the vaporized fuel leaks from the path, the vaporized fuel processing apparatus closes an atmospheric port of the canister in order to apply negative pressure to a place where the vaporized fuel leaks. As a result, the leak of the vaporized fuel into the atmosphere can be prevented. While, another vaporized fuel processing apparatus uses a stepping motor type closing valve, which can control the open amount of the closing valve linearly.
In a case of the stepping motor type closing valve, there is a possibility that a stepping motor break down may be caused by step-out (i.e., where the actual position of the stepping motor and associated valve does not correspond with the assumed position of the motor and valve by the controller or controller unit). In a case that a device having a stepping motor is used, when the stepping motor steps out, the stepping motor is usually initialized and is restarted. In a case of the vaporized fuel processing apparatus, when the stepping motor steps out during working of the vaporized fuel processing apparatus, the stepping motor is caused to be in an initial position such that the stepping motor type closing valve is open or closed. Thus, there is a possibility that the amount of the vaporized fuel flowing into the internal combustion engine suddenly changes, and that the air-fuel ratio in the internal combustion engine becomes disturbed. Accordingly, there has been a need for improved vaporized fuel processing apparatuses.